Abrasive machine and method



Aug. 22, 1961 R. A. WHITAKER 7,

ABRASIVE MACHINE AND METHOD Filed Sept. 9, 1958 69 Fag-.2

g" Hydraulic Mofor United States Patent C hro Filed Sept. 9, 1958, Ser. No. 760,019 3 Claims. (Cl. 204-209) This invention relates to an abrasive machine and method and particularly to a method and means for machining turbine blades and the like.

It is an important object of the present invention to provide a method and means for machining turbine engine airfoil contours with minimum tool pressures.

Another important object of the invention is to provide a novel and improved contour grinding machine and method for turbine blades and other articles having very small transverse strength.

A more specific object of the present invention is to provide an improved endless belt type grinding machine for forming turbine blades and the like.

Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic fragmentary side elevational view of an abrasive machine in accordance with the present invention;

FIGURE 2 is a diagrammatic plan view of the system of FIGURE 1 with certain parts broken away and in section; and

FIGURE 3 is a fragmentary elevational view of an abrasive belt for use in the system of FIGURES l and 2.

As shown on the drawings:

The present invention is directed to the grinding of workpieces having very small transverse strength such as turbine blades. By way of example, the workpiece 10 may be mounted by means of a work holder 12 during the abrading operation and rotated by means of a hydraulic motor 14 and drive spindle 15 as diagrammatically indicated in FIGURE 2. The work may rotate in the direction of the arrow 17 shown in FIGURE 1 and may be traversed longitudinally as indicated by the arrow 19 in FIGURE 2 by any suitable feed mechanism. The workpiece 10 may be secured in the work holder by any suitable means such as indicated at 22 which accommodates rotation of the workpiece in operation of the machine and which is adapted to be releasable for replacement of a finished workpiece with another workpiece to be machined.

The abrasive means may comprise an abrasive endless belt 30 which travels over a backing roll 32 and idler rolls 33 and 34 carried on a frame 36 and is driven by means of a pulley 38 on a shaft 39 of a motor 40. As the workpiece 10 rotates in the direction of the arrow 17, the belt support frame 36 must move generally in the direction of the arrow 42; for example the frame 36 may move arcuately about the axis of drive pulley 38 with the frame 36 mounted on a pivot shaft coaxial with the motor shaft 39. In present commercial practice, the rotational movement indicated by the arrow 17, the axial feed of the work indicated by the arrow 19 and the corresponding movement of the support frame 36 indicated by arrow 42 are all accomplished by an automatic machine. Such a machine might include an airfoil master cam such as indicated at 50 driven by spindle 51 of hydraulic motor 14 in synchronism with the rotation of the workpiece 10 and having a contour corresponding to the desired contour to be produced on the workpiece. A known commercial machine may also provide a cam follower roller such as indicated at 54 for riding on the surface of See the master cam 50 and controlling corresponding movement of the support frame 36. While in commercial practice, suitable power amplification means may be interposed between the roller 54 and the means for moving the support frame 36; in FIGURE 2, for diagrammatic purposes the cam follower 54 has been indicated as being mounted on an arm 56 which in turn is adjustably carried by means of a coupling member 57 secured to the frame 36 so that the frame 36 is illustrated as moving with the follower roller 54 to produce a contour of the workpiece 10 corresponding to the contour of the master cam 50. Of course the master cam 50 would be supported with the work holder 12 by suitable means corresponding to the means 22 at its opposite end (not shown) so that the master cam 50 would move as indicated by the arrow 19 along with the workpiece 10. For illustrative purposes, it may be assumed that the frame 36 is guided manually as the workpiece 10 is rotated by the motor 14 and traversed in the direction of the arrow 19 by any conventional screw feed mechanism, the feed mechanism being reversible to accommodate a number of traverses of the workpiece by the abrading assembly as desired.

In order to reduce the tool pressure on the workpiece during the forming of the turbine blade, a suitable power supply indicated at 65 has its positive terminal connected to the workpiece 10 as indicated by the line 66 and has its negative terminal connected with the backing roll 32 as indicated by line 67 in FIGURE 2 connected to a series of brushes 69 which are in sliding contact with a slip ring 70 secured to shaft 71 of the backing roll 32. The shaft 71 is insulated from the frame 36 and from support arm 3611 by means of suitable insulating bushings such as indicated at 75. The connections between the power supply 65 and the workpiece 10 and backing roll 32 must be of suflicient capacity to carry a current of the order of 300 amperes.

ductively connected with the line 66, for example by insulating the work holder 12 from the remainder of the machine. A suitable electrolytic fluid may be provided by means of nozzle and supply hose 81, the nozzle 80 being mounted by means of a bracket 82 on the support frame 36. By way of example, the electrolytic fluid may comprise water rendered conductive by the addition of rust-inhibiting salts.

By way of example, the belt 30 may comprise an open weave fabric of insulating material coated with a suitable albrasive as indicated at 85. The electrolytic action could then take place from the backing roll 32 through the open mesh of the belt 30 to the workpiece 10, the belt 30 serving to prevent metal-to-metal contact between parts of opposite polarity. Alternatively, the belt could be a woven metal belt or woven from metal and fabric thread and coated with a suitable abrasive. In this case suitable means would be provided for preventing a direct rnetaLto-metal short circuit from developing between the back-up roller 32 and the workpiece 10 through the metal of the belt. As a further alternative, a fabric belt of insulating material could be coated or impregnated with a conductive adhesive which would then carry the abrasive material. In cases where the belt includes conductive material, it is only necessary to provide for fluid contact with the conductive portion of the belt and for electrical contact between the electrically conductive part of the belt and the electrically conductive backing roll 32. As previously mentioned, means must be provided for preventing short circuit between the metal portion of the belt and the workpiece, for example by separating the conductive part of the belt from the Suitable means, should also be provided for insulating those parts con-- 3 workpiece by means of an insulating fabric material or with an insulating abrasive material.

Summarizing the operation, the motor 14 is energized by suitable supply means including hoses '90 and 91 to rotate the workpiece in the direction of arrow 17' in FIGURE 1. Motor 40 is energized to drive the belt 30 in the direction of the arrow 93 in FIGURE 1. A Suitable traverse mechanism is also energized to move the work holder 12 in the direction of the arrow 19 at the desired rate. Lines 66 and 67 are energized from power Supply 65 and a suitable electrolytic fluid is applied by means of nozzle 80 between the belt 30 and the workpiece 10 to produce the electrolytic removal of material from the workpiece 10 at the desired rate; As the workpiece 10 rotates in the direction of the arrow 17, the belt support frame 36 is moved in the direction of the arrow 42 to accommodate this rotation and to form the workpiece 10 to the desired contour. This movement of the support frame 36 has been diagrammatically indicated as being controlled by means of a master cam 50 in conjunction with a cam follower roller 54 mechanically coupled to the support frame 36.

The illustrated machine and method are especially adapted for very small thin turbine blades which have substantially no transverse strength. It is found that 90% of the material removed from the work blank by the machine results from the electrolytic action while 10% is removed by the abrasive action of the belt 36'. It is found that best results are obtained when the electrically charged back-up wheel 32 acts on the electrolytic liquid through an open mesh non-conductive belt such as shown in FIGURE 3.

It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

1. In an abrading machine, an abrasive belt, means for supporting said belt in operative relation to a workpiece, means for moving said belt progressively over said supporting means, and means for producing an electrolytic current at the region of operation of said belt with respect to said workpiece for electrolytically removing material from the workpiece, said belt being of open mesh configuration coated with an abrasive material and having means for insulating said belt supporting means from metal-to-metal contact with said workpiece.

2. In an abrading machine, an abrasive belt, means for supporting said belt inoperative relation to a workpiece, means for moving. said belt progressively over said supporting means, and means for producing an electrolytic current at the region of operation of said belt with respect to said workpiece for electrolytically removing material from the workpiece, said belt being of woven conductive material in electrical contact with said belt supporting means and for electrical contact with an electrolytic fluid interposed between said belt and said workpiece. V g

3. In an abrading machine, an abrasive belt, means for supporting said belt in operative relation to a workpiece, means for moving said belt progressively over said supporting means, and means for producing an electrolytic current at the region of operation of said belt with respect to said workpiece for electrolytically removing material from the workpiece, said belt being of insulating material impregnated with a conductive adhesive carrying abrasive particles at its operative surface, and said conductive adhesive being in direct electrical contact with said belt supporting means and being adapted for electrical contact with an electrolytic liquid interposed be tween the belt and the workpiece.

References Gited in the file of this patent UNITED STATES PATENTS 2,071,563 Newcomb et a1 Feb. 23, 1937 2,332,329 Maca Oct. 19, 1943 2,526,423 Rudorfi' Oct. 17, 1950 2,575,656 Coe et al Nov. 20, 1951 2,587,603 Czarnecki Mar. 4, 1952 2,755,604 Jameson July 24, 1956 2,826,540 Keeleric Mar. 11, 1958 FOREIGN PATENTS 854,224 France Jan. 4, 1940 518,310 Canada Nov. 8, 1955 

1. IN AN ABRADING MACHINE, AN ABRASIVE BELT, MEANS FOR SUPPORTING SAID BELT IN OPERATIVE RELATION TO A WORKPIECE, MEANS FOR MOVING SAID BELT PROGRESSIVELY OVER SAID SUPPORTING MEANS, AND MEANS FOR PRODUCING AN ELECTROLYTIC CURRENT AT THE REGION OF OPERATION OF SAID BELT WITH RESPECT TO SAID WORKPIECE FOR ELECTROLYTICALLY REMOVING MATERIAL FROM THE WORKPIECE, SAID BELT BEING OF OPEN MESH CONFIGURATION COATED WITH AN ABRASIVE MATERIAL 